I'm using a Mac, iMic and fldigi V3.23.00. It appears everything is set correctly, but I'm not making RF.
I can't set the ALC to 4 solid with the 5th bar flickering. The minimum number of bars is a solid 5, the line in at that point is 4. It makes no difference if the iMic is set to Line or Mic. The audio cables are stereo.